About a dozen former prisoners who were released from Guantanamo Bay have killed six Americans and have attacked American and coalition forces in Afghanistan, according to a new report.

The Washington Post cites current and former U.S. officials who say the ex-prisoners have returned to the battlefield since they’ve been released.

One of the Americans killed, according to the Post, was a female aid worker who perished in 2008. Nine of the former prisoners implicated in the attacks, reports the Post, have either been killed or are in custody with governments other than the U.S.

The newspaper cites officials who said the number of prisoners who returned to fight was less than 15. They were all released during President George W. Bush’s administration.

The report follows remarks by Paul Lewis, the Pentagon’s special envoy for Guantanamo detention closure, who said in March ex-Gitmo prisoners have killed Americans.

House Foreign Affairs Committee chairman Edward R. Royce, a California Republican, said in a statement he would like to see President Barack Obama stop releasing Guantanamo Bay prisoners.

"The administration is releasing dangerous terrorists to countries that can’t control them, and misleading Congress in the process," Royce said, reports the Post. "The president should halt detainee transfers immediately and be honest with the American people."

"A recent news report citing U.S. officials who believe at least 12 former Guantanamo Bay detainees launched attacks that resulted in the deaths of about a half-dozen Americans is disturbing," Johnson said in an e-mailed statement. "Even one death is one too many. The American people deserve a government willing to be honest and transparent in the face of the global threat of terrorism.

"There are 80 detainees left at Guantanamo Bay — the worst of the worst. Information regarding these transfers should be public, not hidden by unnecessary classification. I urge my colleagues to support my amendment to the National Defense Authorization Act requiring transparency from the Obama administration on the remaining Guantanamo Bay detainee transfers."